Known automobile theft prevention devices are set or activated when an automobile door is locked through means of a predetermined procedure, for example, by using a key to the door lock or closing the door after the inside knob thereof is depressed (keyless locking). When the engine hood of the automobile is opened while the theft prevention device is in an activated state, the theft prevention device produces an alarm sound. For example, if a thief breaks a window glass panel, enters the automobile, and operates the engine hood lever so as to open the engine hood, then the theft prevention device produces an alarm. When a door is unlocked using a proper means such as, for example, a key to the door, the theft prevention device is inactivated, and no alarm is generated by opening the engine hood thereafter.
The conventional automobile theft prevention devices, however, do not prevent the engine hood from being opened at any time by operating the engine hood lever located within the passenger compartment. Therefore, unauthorized entry into the passenger compartment of an automobile which is equipped with an automobile theft prevention device of the type described, and subsequent operation of the engine hood lever so as to open the engine hood would involve the same theft procedures as would similarly be conducted in connection with an automobile having no such automobile theft prevention device incorporated therein, the only difference being that an alarm is generated when the engine hood is opened. If the alarm was ignored by the thief, therefore, parts in the engine compartment could still be stolen.